On my grade school's trip to an aquarium, I couldn't understand how the whale didn't sink from its own weight. I feel the same about Samuel D. Hunter's The Whale. The writing, design, even the lead actor are wrapped in heavy layers, both literal and symbolic. The play opens with 600-pound Charlie suffering what seems to be a heart attack, and then things take a turn for the worse: Barring some massive turnaround, Charlie's got less than a week to live. Somehow, though, Davis McCallum's production remains buoyant. This Whale floats.

As the days tick down through thick and not so thin, we wade through allusions to Moby Dick and Jonah, and every scene break brings sounds of crashing waves. But this is far from a crushing bore. Undercurrents of dry humor and wry emotion keep things bubbling along. The aforementioned cardiac episode occurs while Charlie's watching Internet porn and fending off a visit from a door-to-door Mormon. One's heart may sink a bit when the young Elder appears. Many of them have been knocking on stage doors these days and that's far from the only common trope in use here. Charlie's main goal is reconnecting with Ellie, the teenaged daughter he hasn't seen since he came out of the closet when she was a toddler. We've seen countless family-reconciliation plays and lots of closed-off girls like Ellie, but even when The Whale wanders into heavily fished waters, it still comes up with fresh revelations and bracing truths.

Shuler Hensley performs the heaviest lifting without any sign of undue strain. He plays Charlie from inside a wondrous body suit designed by Jessica Pabst. Perhaps only Albert Innaurato's The Transfiguration of Benno Blimpie, also about an overweight man, and Samuel Beckett's classic Happy Days, with its lead woman covered up to her neck in sand, have similarly forced a lead actor to use so little of his or her own frame. Charlie's drowning in his own flesh, but Hensley makes sure there isn't a smidge of self-pity. Instead, he blessedly finds a touch of grace.

The rest of the cast is equally direct, when any grandstanding could capsize the production. Cory Michael Smith, who made waves a few months ago as the wavering lover in Cock, does wonders with Elder Thomas, whose path through the play becomes increasingly compelling. Reyna de Courcy seems a touch too old, but keeps us asking whether Ellie is irredeemably hateful or blisteringly honest. De Courcy also impresses by giving a remarkably different performance from her crippled sister in last year's hot-button play Burning. Cassie Beck, who specializes in tender no-frills truth tellers, maintains a toehold on the thin line between empathy and enabling as Charlie's friend and nursemaid. Tasha Lawrence, making a late but indelible appearance as his ex-wife, moves blisteringly from bruised resentment to warmth.

There's a boatload of pain here, and we might consider jumping ship without constant assurance that we're in good hands. McCallum and Hunter command our confidence from the start. Mimi Lien's scenic design presents a pre-fab apartment that reeks of neglect down to the sorriest detail. With a full ceiling and sidewalls, we've got a diorama of despair. Tall ellipses on either side give the sense that the room is a belly within a whale. We identify Charlie with Jonah before any mention of the Bible. And that's all the conceptualizing The Whale needs. I wish that title were less abstract. And there's too much symmetry in Charlie's backstory. He'd left his family to start a new life with Alan, a former student. They shared a blissful decade until a traumatic return to his family's Mormon church led Alan to starve himself to death. Out of grief and guilt, Charlie's now eating himself to death. Fortunately, nothing else feels so schematic.

Hunter embeds talk of Moby Dick and the Bible into the natural fabric of the piece. Charlie, a former high school teacher, now makes a fine (and funny) living tutoring online. He has a special fondness for an old paper on the Melville novel and, when he thinks he's dying at the start, intriguingly asks Elder Thomas to read it to him. Hunter ties up this and other loose ends with invention before the play reaches its final destination in a moment of exhilarating transcendence. Hunter ultimately lands his prey and our affection. This young writer's clearly got big fish to fry, and I look forward to a steady stream of hearty meals.

The Whale runs at Playwrights Horizons' Peter Jay Sharp Theater through December 15. For more information, click here.